1. Field of the Invention
This invention relates to a semiconductor chip carrier for use with very high speed large system integrated circuits and systems for providing superior electrical performance packages for such high speed switching.
2. Description of the Prior Art
In the prior art, integrated circuit chips have continually been applied to increasingly higher frequency operations. The frequencies now being utilized are less than a nanosecond in speed. As is known, at such speeds, the interconnecting network is a transmission line designed for a specific characteristic impedance in order to optimize signal propagation speed, integrity and also to minimize reflections which occur when a discontinuity of the strip line or micro-strip line occurs.
To accomplish this, not only must the module substrate, such as the printed circuit board or the like, have controlled transmission line properties, but also the lead frame of the integrated circuit package should be placed as close to the chip itself as possible. If the gap in the reference plane is less than one quarter of a wave length of the signal no noticeable reflection occurs. At the present speeds which are being approached with use of integrated circuits, the rise and fall times equal a fraction of a nanosecond.
In order to form a transmission line, a conductor is required which is properly spaced from a large conductor with the proper dielectric therebetween. By adjusting the area and thickness for a given dielectric constant one can design a correct impedance transmission line. In integrated circuit packages, the lead from the outside of the package of the chip is frequently larger than one quarter of the wave length of the input signal and therefore provides a discontinuity. To provide a center region in the dielectric for chip attachment that is sufficiently flat, thick materials must be used. When the materials are thick it is not possible to have low impedance because this requires a thick dielectric. The transmission line includes a lead frame and a ground plane separated by a dielectric.